1. Field of the Invention
This invention relates to a polyimide resin composition, more particularly to a polysiloxane-grafted polyimide resin composition. This invention also relates to a flexible substrate formed from the polysiloxane-grafted polyimide resin composition.
2. Description of the Related Art
Recently, organic polymer materials have been widely used in various electronic components or devices so as to enhance various characteristics (for example, electrical insulation, heat resistance, mechanical property, etc.) of the electronic components or devices. Among them, polyimide polymer is most widely used in view of good mechanical and electrical properties. However, it is increasingly required to raise the properties and performances of the electronic components or devices in the art. Therefore, the mechanical properties (for example, flexibility, extensibility, etc.), the thermal properties (for example, low thermal expansion coefficient), insulation, or adhesion of polyimide polymer are required to be improved.
Conventionally, the physical properties, especially thermal or mechanical property, of polyimide polymer are modified by adding various reinforcing materials so as to enhance the applicability of polyimide polymer. Commonly used reinforcing materials include titanium dioxide, silicon dioxide, talc, etc. However, such a modification manner has problems in mixing homogeneity and compatibility. Furthermore, a flexible substrate formed therefrom may have a cloudy appearance.
JP2005-146213 discloses a silane modified polyimide siloxane resin composition useful as an adhesive for a printed circuit board. A polyimide siloxane resin containing a carboxyl group and/or an anhydride group is formed by subjecting a tetracarboxylic dianhydride compound, a dihydroxyl siloxane compound, and a diamine compound to a reaction. An epoxy group-containing silane partial condensate is then added. The carboxyl group and/or the anhydride group of the polyimide siloxane resin react with the epoxy group of the silane partial condensate so as to bond the silane partial condensate to the tetracarboxylic dianhydride moiety of the polyimide siloxane resin and to obtain the silane modified polyimide siloxane resin. However, the silane modified polyimide siloxane resin has inferior thermal stability. The silane partial condensate tends to split from the polyimide siloxane resin which results in impaired mechanical and thermal properties of a flexible substrate formed from the silane modified polyimide siloxane resin composition. Therefore, a flexible substrate obtained from the silane modified polyimide siloxane resin composition may not have satisfactory mechanical and thermal properties, especially when being used for a flexible liquid crystal display or a flexible electronic book.
It is desirable in the art to provide a resin composition for forming a flexible substrate having satisfactory mechanical and thermal properties for an electronic device.